As the use of personal computers became versatile, the memory size requirements have increased. Not only the physical but also external memory such as a floppy disk is required to hold mega bytes of information. However, the certain use of computer graphics and high-fidelity audio in the multi-media computing requires an even larger memory capability in memory devices. For example, a CD-ROM (Compact Disk Read Only Memory) disk stores approximately 600 mega byte of data. Other large capacity memory media include DVD (Digital Video Disk) for storing animation data, a DAT (Digital Audio Tape) for storing digital audio and a MD (Mini-Disk) for storing digital data.
To use these different media, a specific input and output (I/O) device is necessary for each medium. For example, a CD-ROM drive is required to access data stored on a CD-ROM while a DVD drive is necessary to access data from a DVD. In addition to these specific hardware, specific software interface is also necessary. As the term multi-media indicates, the various I/O devices and interfaces are unavoidable in a certain computer systems, and these specific I/O devices add complexity to a computer system.
In addition to the specific I/O requirements, the above described media also have various data formats. The same information is stored in a different format based upon a medium where the information is stored. Furthermore, to make the matter more complicated, within the same application area such as computer graphics, even if the same medium is used, there are numerous data formats to store the same graphic image. Although various data formats are not always easy to manage, conversion programs generally allow sharing of the same data.
In order to eliminate the above described problems associated with the multi-media, a single memory medium has been considered. Such a memory medium has to offer a number of advantages including a large memory capacity, fast access, flexibility and versatility. In view of these considerations, a PC memory card has great potential for the above enumerated desirable characteristics.
Among other things, PC cards have the following advantages when they are used as memory cards: Firstly, the memory cards do not require a specific I/O drive. This is a significant advantage since a memory card does not require any substantial mechanical parts such as a motor and a movable head. Because of the motor less access, many control mechanisms are also unnecessary. Secondly, because no head contacts the memory storage surface, the medium is free from mechanical damage. Thirdly, the memory access is faster since no moving part must be physically moved to access a certain portion of the memory. Although no single memory card does not yet have the memory capacity comparable to a CD-ROM, the memory capacity limitation of a memory card has been steadily improved. For example, the use of bear memory chips helps the chip density on a memory card, and the memory capacity of a memory chip is currently increasing at a rate of four times every three years.
The use of the PC cards have steadily increasing with portable computing. Some commercially available PC cards are used as a portable data storage unit. For example, the memory is a ROM for storing information such as fonts for printers and audio such as music as disclosed in Japanese Patent 59-92482. Other commercially available PC cards are used as devices rather than a memory storage. For example, fax modem cards or communication cards have been widely used for Internet access.
To support the above described various functions performed by the PC cards, Japanese Utility Model Patent 2-110098 discloses that each PC card has two separate memory areas. One is a general purpose area where program code or data is stored to perform a predetermined function. The other memory area is an attribute or configuration memory area where information or identification of the card is stored, and the attribute memory area is accessible only when a predetermined signal is enabled. The above described two-memory area configuration is standardized in the interface protocols such as PCMCIA (Personal Computer Memory Card International Association), JEIDA (Japanese Electronics Industry Development Association) as well as PC Card Standard (1995), which is jointly developed by PCMCIA and JEIDA. Also, see "A Summary of the Most Recent PC Card Standard" in Japanese, PP89-95, Interface, June, 1995. The two independent memory design is not efficient way of managing input/output of these PC cards especially when a plurality of memory cards is to be managed. Furthermore, the same address value is not unique in the above two-tier memory design. Depending upon the status of the predetermined signal, the same address resides in either of the two address areas. These address related issues are particularly important when a PC card is used as an expanded RAM device or a ROM data storage device.
To solve the above and other problems and improve the management of the PC cards, there has been a need for efficient memory card management systems and methods.